It has been known for many years that when rime forms on cultivated plants at the moment when ambient temperature reaches 0.degree. C., these plants are then protected against frost by the rime layer. In fact, the formation of rime on the plant prevents radiation from the plant leaves and the heat loss thereof, through a white body effect.
However, when the dew point is zero 0.degree. C. or less than zero, frost occurs before the plant is covered with dew. Rime will therefore not form, and the plant will further radiate its heat content away when the ambient temperature reaches 0.degree. C. and below. The plant will then freeze.
In order to prevent cultivated plants from freezing in such a case, a current practice is to spray them with water when the temperature is nearing 0.degree. C., so as to obtain the protecting rime when the temperature reaches 0.degree. C.
This implies a continuous monitoring of the evolution of the local weather, particularly of the ambient temperature and of the dew point, during periods when frost may possibly occur, and it further implies that spraying should be initiated at the appropriate time by the farmer.
Another problem also arises with plants for which the reproduction temperature is largely above the freezing temperature. For instance, in banana tree plantations, growth and reproduction of bananas no longer takes place after the ambient temperature has dropped below 16.degree. C.
In countries where this is likely to occur, there will be no crop if, at the reproduction time, temperature has dropped below the 16.degree. C. threshold.
This invention aims at overcoming these drawbacks by providing a method for automatically maintaining, through a constant monitoring of local weather conditions, on the one hand the dew point at an acceptable value for rime to form on the plants at the time of frost occurrence, and on the other hand, more particularly in cases in which temperature should not drop below a certain determined value according to the kind of plants cultivated, a micro-climate presenting the required qualities for facilitating the reproduction and growth of plants, and more particularly a formation of dew.